The new Audi S8 has a twin turbocharged V8 engine in place of its predecessor's naturally aspirated V10 - but is it any more fun to drive?

Audi’s new range-topping super-saloon, complete with a twin-turbocharged 4.0-litre V8 engine in place of the previous S8’s 5.0-litre V10. We’ve already had a brief go in a pre-production prototype, but this is the first chance we’ve had to put the finished car through its paces.

The script may be familiar from other S-branded Audis – serious power, in this case 512 bhp, blistering on-paper performance – the official 0-62mph time is just 4.2 seconds – and Audi’s quattro four-wheel drive system to try and keep everything pointing in the right direction.

Where it differs is the emphasis put on mpg and CO2, with the new engine using a clever selective cylinder shut-down system, and claimed to improve combined economy to 27.7mpg.

Sales will start in the UK next spring, and although final prices and specs have yet to be confirmed, Audi reckons the car will be on sale for ‘around £80,000’.

Technical highlights?

The new engine is a very serious bit of engineering – not least because its development marks the end of Audi’s relatively brief dalliance with the naturally aspirated V10 of the previous S6 and S8.

The 4.0-litre V8 uses two twin-scroll turbochargers mounted in the vee of the cylinder bank to improve responses, and combines its peak 512bhp with a very solid 479bhp of torque – with this peak available all the way from 1700rpm and 5500rpm. Drive is supplied via an eight-speed automatic gearbox, plus Audi’s new ‘sport differential’, intended to sharpen cornering response by vectoring torque to the outside rear wheel. The S8 rides on air springs, with all versions getting three-stage variable damping.

The fuel-saving tech is likely to get most headlines, although in truth it’s a relatively small part of the S8’s box of tricks. Under light use when coasting the engine automatically deactivates cylinders 2, 3, 5 and 8 – this can only happen when the engine is producing less than 185lb ft, the car is in third gear or higher and the engine is turning at between 1000 and 3500rpm. When the conditions are met, lobes on the camshaft slide to engage ‘zero lift’ lobes next to the cylinders to be deactivated. The system can then fire up the idle cylinders on demand, in just 0.3 seconds.

What’s it like to drive?

The cylinder deactivation system is something that most drivers will barely notice. Not only is the switch between eight and four cylinders effectively invisible, the only indication is a small message on the dashboard display, but in real world driving you’re only likely to experience it under very gentle use – anything more than very gentle pressure on the throttle pedal is enough to turn the V4 back into a V8.

It’s certainly quick. The new engine lacks the high-revving drama of the old V10 – peak power arrives at just 5800rpm and the engine revs out barely past the ‘6’ mark on the tacho. But the combination of instantaneous torque and the autobox’s clever brain makes for some spectacular blue touchpaper moments. Acceleration is relentless and seemingly linear – barely abating as speeds turn from silly to outright daft. Like the standard A8, the cabin is extremely well insulated and – in any of the three suspension modes – the ride is comfortable and body control good. In short, the S8 looks set to be a brilliant high-speed cruiser – if you had to cross Germany in a single sitting, this would be the tool for the job.

Sadly, when it gets to the business of corners, we’re quickly brought back to the established S-badge script. On faster sweepers its fine – you wouldn’t say the car disguises its two-tonne kerbweight, but there’s lots of grip and a commendable willingness to stick to a chosen line. But on slower stuff the S8 quickly starts to feel nose heavy, with faster progress becoming a question of managing understeer more than anything else. The Sport Differential can be felt to be doing its thing by vectoring torque to the outside rear corner – deactivate the stability control and its even possible to persuade the S8 into a distinctly un-Audi like tailslide at low speeds. But this feels like a dynamic sticking plaster rather than a full cure – it’s completely without the sense of flowing, give-and-take you get from driving a BMW M5 similarly hard.

How does it compare?

Audi is keen to steer comparison of the S8 towards the Mercedes S63 AMG and Jaguar XJ Supersports – both of which are considerably more expensive. In truth, a better comparison might be found in the just-launched BMW M5, which is only £10,000 less expensive and similarly rapid. And it’s a contest that – for anyone who doesn’t have rear seat space at the top of their selection criteria – will find the Audi lacking.

On the plus side, the S8 is extremely well equipped and as well built and engineered as you’d expect any modern Audi to be. And if it does arrive with an £80,000 pricetag then it will look like good value against a fully-optioned A8 from further down the range.

Anything else I need to know?

Carbon ceramic brakes are an option, and were fitted to our test car. They provided tireless retardation under fast road use, although they started grumbling when they got hot.

An ‘antiphase’ noise-cancelling system is fitted in the cabin to cancel out any unwanted harmonics when running in four-cylinder mode, although in real world use it’s effectively invisible.

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